In high-pressure tanks which are to be charged with gas such as hydrogen, gas tightness is important. Concerning this type of gas tank, there is known, as technology for establishing a seal between a mouth portion formed on a resin liner forming a tank body and a ferrule member fitted on the inner peripheral side of the mouth portion, technology in which an O-ring is mounted in a groove portion formed on the liner and an insert ring is provided on the outer periphery of the liner for clamping the O-ring in the radially inward direction, thereby establishing a seal between the mouth portion and the ferrule member. (See JP 2008-303966 A, for example).
Further, there is also known, as technology for establishing a seal between the mouth portion and the ferrule member, technology in which an O-ring is mounted in a groove portion formed on the outer periphery of a ferrule member and an insert-ring (backup ring) is insert-molded within a liner to thereby establish a seal between the mouth portion and the ferrule member. (See JP 2005-48919 A)
However, with regard to the insert ring which is used for the tank described in JP 2008-303966 A, there is a problem that there are cases in which, at the time of molding the liner, the volume of a resin (charging quantity) charging the inner peripheral side of the insert ring differs from the volume of a resin (charging quantity) charging the outer peripheral side of the insert ring, and consequently the insert ring is fixed in a displaced (off-center) state with respect to the center axis of the cylindrical mouth portion.
Further, with regard to the tank described in JP 2005-48919 A, when there is a difference in dimension between the liner mold die and the insert ring, the insert ring is fixed in a displaced (off-center) state with respect to the center axis of the cylindrical mouth portion by resin flowing at the time of the liner molding.
When the insert ring is fixed in an off-center state as described above, the thickness of the resin provided between the insert ring and the mouth portion becomes non-uniform (in the circumferential direction).
Further, when the thickness of the resin provided between the insert ring and the mouth portion is non-uniform, the liner (mainly the mouth portion) is deformed due to a reaction force of the O-ring, thereby preventing securing of sufficient sealability between the mouth portion and the ferrule member.